Vintage analog medical telemetry from the 1970s exhibited a typical maximum data loss of 50 minutes per day—an enormous improvement over no patient monitoring. The initial digital systems stumbled as they exhibited 75 minutes per day of lost data. Over time improvements were made, but second generation Ultra High Frequency (UHF) telemetry, including most systems running in the Wireless Medical Telemetry Service (WMTS) still exhibited 25 minutes of dropout per day.
The medical world received a wakeup call when a High Definition Television (HDTV) station test near the Baylor Hospital impacted patient telemetry. If a digital television station transmits in the same channel as UHF telemetry, virtually no data are transmitted successfully, which is why the Food and Drug Administration (FDA) and Association for the Advancement of Medical Instrumentation (AAMI) petitioned the Federal Communications Commission (FCC) for a band dedicated to medical telemetry, resulting in the Wireless Medical Telemetry Service (WMTS). This allocation precludes a television station using the dedicated band, but does not result in any improvement over the 25 minutes/day of dropout
Some companies have improved on second generation digital telemetry systems by copying the 802.11 Access Point (AP) concept, including using spread spectrum technology. With any spread spectrum technology, the high ratio of available bandwidth to data bandwidth is important, but the widest band of the WMTS spans only 6 MHz. As a result, spread spectrum systems that use this band render useless nearby second generation systems also in this band. Other Wireless Medical Telemetry Service solutions include re-crystalling existing systems. While this expensive “upgrade” removes the worry of an in-band HDTV station, it does nothing to improve the 25 minutes per day of dropout. Philips uses the yet-smaller 1.4 GHz band of the WMTS with channels limited to only 12,500 bps at a range of 30 feet.
About the same time as Wireless Medical Telemetry Service was being considered in 1999, IEEE 802.11 standard was ratified. Some medical companies embraced the concept of standards-based solutions as a means to make better use of networks by sharing one network among many applications. At that time, the promise was unrealized because standards and protocols for security and quality of service had not yet been developed. What 802.11 brought was a 10-fold decrease in dropout [S. D. Baker, et al., “Performance Measure of ISM-Band and Conventional Telemetry,” IEEE EMBS, vol. 23, pp. 27-36, May/June 2004] that is realized because of a robust modulation, intelligent communication protocols, and good radio frequency network design.
Since then, wireless Local Area Networks (LANs) have become ubiquitous in many industries and even within the cautious healthcare environment: nearly 50 percent of hospitals have 802.11 LANs installed and over 80 percent are planning to have an 802.11 networks deployed to support Electronic Medical Records (EMR) within the next two years.
Market forces, including demand for toll-quality wireless Voice over Internet Protocol (VoIP) and secure communication, resulted in supplementary standards that allow multiple applications to securely (802.11i) share an Access Point with protection for critical data transactions (802.11e). Thin Access Point architectures allow information technology staff to manage the entire wireless network from a single point. Chipsets supporting the 802.11a physical layer have been available for several years and infrastructures are now typically installed with 802.11a/g support. In fact enterprise-class solutions are only available with 802.11 a/b/g chipsets (Concurrent with the rise of 802.11 a/b/g chipsets came the last of 802.11b-only radios. Some institutions now ban 802.11b and use 802.11g or 802.11a/g only.). In the United States, the FCC recently augmented the 802.11 a band with an additional 255 MHz of bandwidth resulting in a total of 555 MHz, for a total of 21 non-overlapping channels. This is more than all bandwidth allocated for broadcast television, AM and FM radio, Cellular, and Personal Communications Service (PCS) combined. Just as One megawatt Effective Isotropic Radiate Power (EIRP=transmit power*antenna gain) TV stations spaced hundreds of miles apart can re-use each TV channel, 200 milliwatt EIRP 802.11 Access Points spaced hundreds of feet apart can also re-use each 802.11 channels. The 802.11a APs' EIRP is 5 million times smaller than that of TV stations. Because channels of this power difference, the 802.11 channel re-use is measured in tens of meters and APs channels can be re-used every 150 feet or so. This results in a bandwidth only limited by the size of the hospital and the speed of the information technology backbone.
Many hospitals have already identified multiple applications that can share a single 802.11 network. Some hospitals justify the cost of an enterprise-wide 802.11a/g network upgrade simply to meet the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) requirements for Bar Code Medical Administration (BCMA) where a patient's identification and medications are scanned prior to administration, with the data verified by a server on the other side of a wireless LAN.
Table 1 shows some of the network-communication applications in use in hospitals and a summary of what wireless solutions exist to support these applications on an enterprise scale. Note that 802.11g can be used without much issue at the unit or department level, but with only three non-overlapping channels, it is not well suited for enterprise installations because of the difficulty in laying out a network without neighboring APs sharing, and therefore interfering on the same channel. If one attempts to have redundant coverage, where multiple APs provide RF coverage of the same area, then 802.11b/g is not suitable. Still the concepts embodied in this patent pertain to both 802.11g and 802.11b networks.
TABLE 1Wireless Solutions and Applications802.11a802.11g1CellularPagingPLMRWMTSMICSBluetoothNurse Call•••Voice••••2•3Telemetry••••BedsidePatient••••MonitoringClinicianAlarm•••NotificationBCMA••Remote Access•••Guest Access••EMR/CIS••ApplicationsStreaming••Video4E-mail•••Location•••5Cart on Wheels••Backup•6••2CommunicationImplanted•DevicePatient Billing••SupportsRedundant••••CoverageGeographicEnterprise/Unit/WorldWorldUnit/Unit/RoomRoomScaleCampusFloorFloorFloor1802.11 b/g solutions work on a limited scale, e.g., for a single hospital unit with minimal traffic, due to the limited number of 3 non-overlapping channels.2Since PLMR does not use a network, it is a good emergency backup, but communication across the enterprise is not guaranteed. Private calls are not supported.3Headset to earpiece only4VGA resolution at 30 frames per second or better5Outdoor location only - indoor GPS service is not dependable because S-Band doesn't penetrate through floors and walls well.6With redundant installation and backup power installed
The primary advantage and rationale for these technologies being deployed in the healthcare enterprise is due to the technologies being highly mobile. Healthcare facilities are one of the most communications intensive environments that exist today. Many devices already in use including laptop computers, personal digital assistants (PDAs), cellular phones, infusion pumps, and patient monitors now come with embedded 802.11 radios. Moving forward, we see that one cost effective way for improving work flow, productivity, and patient outcomes will involve using tools such as Wireless VoIP, PDAs supporting applications such as drug formularies, nurse-call, and patient-clinician alarm notification, and Patient monitoring on an enterprise-wide network that has been designed for the intended use. Without this, patients are at increased risk for not being continuously monitored, and clinician's frustration with not being able to use the wireless services for their clinical needs will continue to increase. Clinicians should be able to access and update patient records including medications at the bedside, rather than going out into the hall where the Cart on Wheels (CoW) has wireless access or even back to the nurse's station. Wireless VoIP, which can be used for paging, as a walkie-talkie, or as a phone to dial long distance requires a higher radio frequency coverage level than is required for downloading e-mail.
Hospitals are a challenging radio frequency (RF) environment with shielded rooms, significant amounts of RF-reflective metal (food carts that interrupted conventional telemetry), and a high availability requirement for all applications. Because of this, a routine wireless installation to simply provide RF coverage appropriate for an office environment is not acceptable. As an example, some early adopter hospitals and wireless installers designed and installed to specifications simply to provide minimum RF coverage, even if this meant occasional dropped packets. Others opted for coverage where clinicians are most of the time. The assumption behind these installations may have been that wireless users would seek out good connectivity locations and these early adopters did not need support for “RF-everywhere” applications such as VoIP. While some people view any and all wireless LAN installations identically, it is not reasonable to ascribe this philosophy to a network that supports life critical applications. Medical device networks intended to support life critical applications, such as physiologic alarms, must use highly reliable networks that result from the verification and validation prescribed by the FDA. A network that simply provides RF coverage most of the time in most areas of the hospital is not acceptable. Proper requirements specification and design is required for the network to reliably support multiple, critical applications throughout the hospital.
As hospitals move toward networks that share resources between information technology (IT) backbones and medical device-based networks to save costs, a there must be a way to ensure that life critical data reach the intended destination with acceptable latency. There are some proprietary solutions that exist, but these unfortunately represent a short term solution as the telecommunication industry continues to follow a strong trend to alight with standards-based solutions, e.g., 802.11e for Quality of Service. While many wireless VoIP manufacturers have been using proprietary Quality of Service, schemes such as always setting the backoff interval to zero, these solutions do not coexist well with non-VoIP data. Similarly, some packet prioritization solutions, such as that offered by Packeteer, provide “traffic shaping”, but these proprietary solutions to optimize WLAN bandwidth have been made obsolete with 802.11e.
Further, as hospitals add additional shared applications on the infrastructure, there is no automatic method for IT managers to determine that the Quality of Service level is sufficient for a given application, That is, they can see that the latency on a given node is a certain value, but must manually determine if the applications running on that node support operation with that latency value. As the IEEE 11073 guidance document for medical transport indicates, it is ultimately the end user's responsibility to ensure that the network meets the timing specifications for all the devices on the network.
Historically, biomedical networks and information technology backbone have run separately with the proprietary biomedical networks managed by the biomedical engineer in close cooperation with the medical device manufacturer. As these networks were not connected to the hospital's IT backbone the medical device manufacturer could configure the network in any manner and typically had access to the network to monitor and/or trouble shoot. With shared 802.11 networks that support the enterprise, these solutions are no longer viable as the hospital information technology departments understandably want to control their own network and are not disposed to giving outside access to these networks. Both network security and Health Insurance Portability and Accountability Act (HIPAA) compliance are issues.
There exist many network tools such as HP Open View, Aruba MMS, CiscoWorks LAN Management Solution for analyzing and diagnosing issues with the IT backbone; however, these are typically not available to the medical device manufacturer nor the clinicians whose patients' safety is at risk. Also, for smaller hospitals, these solutions are cost prohibitive.
What is needed is an economical, standards-based solution that allows medical device companies and/or hospital personnel to diagnose issues that occur on systems that use 802.11 and 802.3 networks while maintaining security and privacy of the network. What is further needed is a method to proactively detect problems and alert clinicians and or information technology personnel on a per-application basis of the issue. The clinician alert must be presented in a way that integrates with the clinician's workflow and preferably presented on a device the clinician uses consistently throughout the day.